The Resource Directory Description Language (RDDL): What goes at the end of a namespace URI?JonathanBordenAssistant ProfessorTufts University School of MedicineDepartment of NeurosurgeryNew England Medical Center #178750 Washington StreetBostonMA02111617-636-5859617-636-7587jonathan@openhealth.orghttp://www.openhealth.orgDr. Jonathan Borden is an editor of the RDDL specification.
He is the Director of the Open Healthcare Group, and a co-chair of the ASTM E31.25 XML Healthcare DTD subcommittee.namespaceRDDLXLinkXHTMLontology
A namespace is properly considered a collection of names. Namespaces while
partitioned by a unique identifier, are properly the collection of names,
not the partition. The XML Namespace recommendation defines a partition
mechanism without defining the mechanism by which names are
collected.
The Resource Directory Description Language (RDDL) was created to answer the
question of what ought a namespace URI reference? RDDL uses an XHTML format in
which resource elements are embedded. Each resource element contains a simple
XLink referencing the related resource.
The use of URIs as a mechanism of namespace partitioning has been controversial
and confusing for several reasons:

For the computer science community: XML namespaces differ from traditional namespaces as traditional namespaces conventionally refer to a set whereas XML namespaces more properly refer to an unbounded partition

For the web community: Use of URIs which can be resolved (i.e URLs) suggests that XML namespace identifiers 'point to something' yet no guidance is provided on what they ought reference.

RDDL is simple, solves both of these problems, and works with
the current Web infrastructure.The Resource Directory Description Language is an extension of W3C XHTML Basic 1.0 with an added
element named resource. This element serves
as an XLink to the referenced resource, and contains a human-readable
description of the resource and machine readable links which describe the
purpose of the link and the nature of the resource being linked to. The nature
of the resource being linked to is indicated by the xlink:role
attribute and the purpose of the link is indicated by the
xlink:arcrole attribute. The rddl:resource element is defined as:<!ELEMENT rddl:resource (#PCDATA | %Flow.mix;)*>
<!ATTLIST rddl:resource
id ID #IMPLIED
xml:lang NMTOKEN #IMPLIED
xml:base CDATA #IMPLIED
xmlns:rddl CDATA #FIXED "http://www.rddl.org/"
xlink:type (simple) #FIXED "simple"
xlink:arcrole CDATA #IMPLIED
xlink:role CDATA "http://www.rddl.org/#resource"
xlink:href CDATA #IMPLIED
xlink:title CDATA #IMPLIED
xlink:embed CDATA #FIXED "none"
xlink:actuate CDATA #FIXED "none"
>

For the computer science community, a proper
namespace is created from an XML namespace as the set of
fragment identifier qualified URI references contained in the RDDL document
describing the XML namespace.

For the web community, a namespace name references a document which is
readable by humans in popular browsers as well as providing machine readable
links to resources related to the namespace. For example an "XML browser" would
be able to locate code or plugins needed for the display of namespace qualified
elements such as embedded SVG, MathML or other formats.The RDDL specification itself serves as a RDDL description of the RDDL
namespace URI http://www.rddl.org/ . RDDL is
described a DTD, and various schemata including RELAX, TREX, Schematron and XML
Schema. In this context RDDL serves as a case study for the development and
comparision of these various schema languages.RDDL is now found at the end of the namespace URI for schema languages such
as Schematron, XML Schema, and Examplotron, and for namespaces such as RSS 1.0,
and the Comminity XSLT Extension effort.Natures and purposes of namespace related resources are defined to be URI
references according to XLink. RDDL defines common natures and purposes. A
discussion of the RDDL ontology, use of RDDL to develop ontologies and
integration of RDDL with RDF/DAML+OIL ontologies is discussed.